Volvox carteri f. nagariensis has an unusual combination of attributes that make it unique for the study of cellular differentiation and development in a simple, multicellular organism. Having only two kinds of cells, somatic and reproductive, Volvox exhibits a developmental pattern which varies depending on whether an asexual, a male, or a female embryo is forming. The control of pattern is through a chemical secreted by the sperm. It is proposed to continue research in the following lines: 1) The nature and biochemical action of the inducer secreted by the sperm will be investigated through various approaches including the genetics of inducer specificity using strains of V. carteri from Australia, U.S., and India; the genetics and physiology of a mutant with a marked reduction in susceptibility to the inducer; and, thirdly, a continuing study of the spontaneous mutants resulting in the formation of sexual embryos without the addition of the inducer. 2) The genetic control of the developmental pattern in the embryo will be studied further using newly isolated developmental mutants in addition to those already in culture, in hopes of elucidating further the steps in the developmental pattern as they may relate to one another. 3) Further analysis of other species of Volvox for systems of induction will involve strains already isolated from many different parts of the world.